Electron microscopical analysis of surface charge labelling density at various stages of the erythroid line.

With use of the positively charged, colloidal ferric oxide labelling technique for electron microscopy of sections of rabbit marrow, a reduction in labelling density on the surface of differentiating red cell precursors was demonstrated. The number of iron particles per unit length of membrane was counted. A progressive diminution in labelling density follows cell division, reaching a minimum in the orthochromatic erythroblast, from which the nucleus is expelled. A slight increase in charge density is noted in the reticulocyte, and further increase is observed with its maturation to the erythrocyte. The results indicate that biosynthesis of n-acetyl neuraminic acid stops at the earliest recognizable stage of erythroid differentiation.